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Full text of "Hacks and Mods"

Add Volume, Jack 



.1 



Make Projects 



build, hack, tweak, share, discover. 



Add Volume, Jack 

Written By: Peter Edwards 



TOOLS: 



Continuity tester (1) 

or ohmmeter or multimeter 

Drill (1) 

or Dremel rotary tool 

Masking tape (1) 

Pencil (1) 

Pliers (1) 

Screwdriver (1) 

Soldering iron and solder (1) 



PARTS: 



Audio toy, mono (single speaker) (1) 
battery-powered or very low amperage 

Potentiometer (1) 

from RadioShack. Some people prefer 
audio taper (logarithmic) pots, but 
regular linear pots work fine, too. 

Switching audio jack, normally closed 
(NC) (1) 

Choose a 1/4" jack for guitar cable or 
1/8" (3.5mm) for mini/headphone plugs. 

• Stranded Wired) 

from RadioShack. 3' total is plenty. 

Resistor 100(1) 

from RadioShack. Optional. Attaches 
across the outer legs of your 
potentiometer if your output is distorted. 
RadioShack #271-013 ($1 for 5). 

KnobM) 

from RadioShack. 



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Page 1 of 7 



Add Volume, Jack 
SUMMARY 

Many cheap, fun sonic and musical toys have built-in speakers and no output jack. This 
limits their volume, unless you constantly hold them up to a microphone. Here's how to mod 
these devices so you can plug them in, adjust their volume, and rock out. 

The simplest way to install an output jack is to remove the speaker and solder the jack in its 
place. But every time I do this I regret it, because then the toy no longer works by itself. 
Inevitably, there will be a time you want to play and there's no amp around. 

You can also leave the speaker connected in parallel with a regular audio jack, but then the 
speaker might act like a microphone and trigger feedback and unwanted noise when you're 
plugged in. 

My favorite solution is to use a switching jack, which automatically disconnects the speaker 
when you plug in a cord. You can also use a non-switching jack and an on/off toggle that 
switches the speaker between standalone and plugged-in modes. But switching jacks are 
only slightly more expensive than non-switching jacks. Why use two pieces of hardware 
when one achieves the same effect? 

Check out more Weekend Projects . 



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Add Volume, Jack 



Step 1 — Identify your jack's contacts. 




• First you need to identify three lugs of the jack: tip, sleeve, and switch. There are many 
different styles of jack available, so it's hard to offer general rules for identifying these. 

• The second image here shows a schematic for this project with one common audio jack 
lug configuration. If your jack varies from this one, look for a spec sheet online. 



Step 2 — Expose the circuit. 




• Open the device and find its 
speaker. 

• To keep screws in a safe place, 
you can usually stick them to the 
speaker magnet. 

• Unless you're experienced 
with electronics, you should 
only work on circuits that are 
battery-powered or use a very low- 
amperage power supply (50mA or 
so). Poking around inside high- 
voltage and/or high-current circuits 
can be fatal. 



A 



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Add Volume, Jack 



Step 3 — Identify the speaker ground and hot signal lines. 




• Two wires connect the speaker to the circuit board: the hot signal that creates the 
fluctuating sound wave and the stable speaker ground that establishes the signal 
amplitude. 

• The ground attaches to the power supply (the negative contact in most pro audio gear, but 
toys can run either way). Once you've identified one wire, you know what the other one is, 
and you can use some tape to mark them both on your board. Here are three methods for 
finding the ground wire: 

• Follow the leads to the power supply. Follow both speaker leads out to see where 
they connect, continuing along traces on the board if needed. Whichever wire runs to 
the power supply is your speaker ground (black ground wire is highlighted green in 
second photo). 

• Use a continuity tester. Most multimeters have a continuity setting marked with an 
image of a speaker or sound waves. Disconnect the speaker, touch one meter probe to 
the positive or negative power supply, and then touch the other probe consecutively to 
the speaker's contact points on the board. The speaker contact with zero resistance to 
either power contact is ground. 

• Look for a transistor or audio amplifier IC. On the board, one of the speaker wires 
probably connects directly to the output of a transistor or an amp IC such as the LM386. 
This is your hot signal. 



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Add Volume, Jack 



Step 4 — Wire up the pot and jack. 




• On your potentiometer, decide 
which leg will be the ground and 
which will be hot (the middle leg is 
always the sweep). 

• Solder wire connections as follows: 
jack tip to pot sweep; jack switch 
to one side of the speaker; jack 
sleeve to the other side of the 
speaker and to pot ground; pot 
ground to speaker ground on the 
board; pot hot to hot output on the 
board. 

• Make the wires long enough to give 
wiggle room for mounting the 
controls. 



Step 5 — Test it! 




• Plug the device into an amplifier 
and play it. 

• If it sounds distorted, solder a 10Q 
resistor between the hot and 
ground legs of the potentiometer, 
as shown here. 

• If the signal is too loud for your 
liking, you can also add a 1Q-10Q 
resistor between the potentiometer 
and the output jack. 



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Add Volume, Jack 



Step 6 — Mount the pot and jack. 






• Choose and mark locations where the volume and output jack can fit on the toy's casing, 
then use a drill or Dremel tool to create the appropriate-sized holes. 

• If you place your holes along a seam, use a high-speed Dremel to remove the 
plastic with a cutting/routing bit. An ordinary drill would simply push the halves 
apart or split the plastic. 

• Mount the hardware and put the knob on the pot. Once that's done, carefully close up the 
housing, but don't screw it back together yet. 







Step 7 — Retest and assemble. 




• In the process of closing the 
housing, it's likely that you moved 
around and possibly severed some 
of your wiring. 

• Test the device again, both 
plugged-in and unplugged, to make 
sure it still works. 

• If so, screw the housing back 
together, and you're ready to rock. 



Adapted from an article by Peter Edwards in MAKE Volume 24. 



This document was last generated on 2012-11-01 08:33:02 PM. 



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Add Volume, Jack 



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